CHARACTERS OF BIRDS. 



387 



invariably consists of two phalanges only. The most internal 

 of the three toes which are directed forwards, consists of three 

 phalanges ; the next has four phalanges ; and the outermost 

 toe is made up of five phalanges (fig. 330, A). This in- 

 crease in an arithmetical ratio of the phalanges of the toes, 

 in proceeding from the inner to the outer side of the foot, 

 obtains in almost all birds, and enables us readily to detect 

 which digit is suppressed, when the normal four are not all 



Fig. 330. A, Hind-limb of the Loon (Colyntbus glacialis) after Owen: i Innominate 

 bone ; j Thigh-bone or femur ; / Tibia, with the proximal portion of the tarsus anchy- 

 losed with its lower end ; r Fibula ; m Tarso-metatarsus, consisting of the distal portion 

 of the tarsus anchylosed with the metatarsus ; p p Phalanges of the toes. B, Tail of the 

 Golden Eagle : j Ploughshare-bone, carrying the great tail-feathers. 



present. Variations of different kinds exist, however, in the 

 number and disposition of the toes. In many birds such as 

 the Parrots the outermost toe is turned backwards, so that 

 there are two toes in front and two behind. In others, again, 

 the outer toe is normally directed forwards, but can be turned 

 backwards at the will of the animal. In the Swifts, on the 

 other hand, all four toes are present, but they are all turned 

 forwards. In many cases especially amongst the Natatorial 



